Bandgap Engineering of Laser-Patterned Diamond-Like Carbon Structures

We report the formation of Si-DLC thin films on Si (100) and sapphire (0001) substrates via plasma-enhanced chemical vapor deposition (PECVD) technique. Subsequently, these thin films were irradiated with nanosecond ArF excimer laser pulses (λ = 193 nm; pulse duration = 20 ns) of varied energy density (0.6 Jcm^-2. 0.7 Jcm^-2, and 0.8 Jcm^-2). The pulsed laser annealing (PLA) technique melts the Si-DLC films in a super-undercooled state that can be quenched rapidly. As such, the sp² content in the films can be modified by controlling the energy density of the laser pulse. We show that the optical bandgap of Si-DLC structures can be controlled by suitably tuning the sp² content in Si-DLC thin films through the PLA technique. Raman spectroscopy and XPS studies were employed to determine the sp²/sp³ ratio in the as-deposited and PLA-treated Si-DLC thin films. Absorption spectra were obtained by UV-Vis spectroscopy and used to determine the optical bandgap (Tauc’s method) and Urbach energy and correlated with the sp² content in the films. This study shows that PLA is a powerful technique for controlling the functional properties of DLC thin films for state-of-the-art optoelectronic applications.